Apparatus for the biological purification of waste water

ABSTRACT

Sewage treatment apparatus which is constituted of an oxygenating tank in which water and sludge circulate upwardly through an elongated member, a pipe connecting the oxygenating tank with a settling tank where the sludge is settled out, and a recirculation pipe returns the sludge from the settling tank to the oxygenating tank wherein means are provided for adjusting the amount of circulating water and sludge to an extent of upward flow which corresponds to the amount of recirculating sludge, for optimum performance of the apparatus under a wide range of operating conditions.

United States Patent Abraham et al.

[is] 3,682,313 [451 Aug. 8, 1972 [54] APPARATUS FOR THE BIOLOGICALPURIFICATION OF WASTE WATER [72] Inventors: Endre Abraham; Laszlo Tasfi,both of Budapest, Hungary [73] Assignee: Tatabanyai Szenbanyak,Tatbanya,

Hungary [22] Filed: March 2, 1970 [21] Appl.No.: 15,416

[52] US. Cl. ..'....210/l95, 210/14, 210/197 [51] Int. Cl ..,....COZcH10 [58] Field of Search ..2l0/195, 197, 3-8,

[56] References Cited- UNITED STATES PATENTS 6/1970 Roos ..210/63 XDurdin ..2 l 0/ l 97 Daniel ..2l0ll97 FOREIGN PATENTS OR APPLICATIONS470,873 8/1937 Great Britain ..2l0/l97 269,469 11/1929 Italy ..2l0/l97Primary Examiner- Michael Rogers Attorney-Gabriel P. Katona [57]ABSTRACT Sewage treatment apparatus which is constituted of anoxygenating tank in which water and sludge circulate upwardly through anelongated member, a pipe connecting the oxygenating tank with a settlingtank where the sludge is settled out, and a recirculation pipe returnsthe sludge from the settling tank to the oxygenating tank wherein meansare provided for adjusting the amount of circulating water and sludge toan extent of upward flow which corresponds to the amount ofrecirculating sludge, for optimum performance of the apparatus under awide range of operating conditions.

3Clailm,3Drawingfigures The invention relates to a process and anapparatus for the biological purification of waste waters with.activated sludge, which permit the recycling of the sludge contained ina setting tank back to the aerating tank without the use of a recyclingpump unit, with intense stirring of the contents of said aerating tankand an abundant supply of oxygen required for the biological processes.

In conventional processes for the purification of household andindustrial waste waters an apparatus for the intense stirring of thewastes to be purified, a reactor tank and a settling tank connected toit are required. The apparatus acting as reactor tank has the purpose ofthoroughly and continuously stirring the mixture of waste water andsludge, and to provide the oxygen required for the biological processestaking place in the mixture. For the purification of industrial wastesthe reactor tank has the task of ensuring the intimate blending of thewaste to be treated together with a reagent. The separation of thecomponents of the mixture, i.e., the settling of the sludge floating inthe mixture takes place in a secondary tank, the settling tank.

In biological purification of waste waters with activated sludge, thesludge settled in a secondary, settling tank is needed as carrier mediumfor the bacteria required in the biological process hence the sledgemust be recycled from the settling tank.

In the conventional apparatus for purifying industrial waste watersrecycling into the reactor tank is required when there is an excessamount of reagent, momentarily present in the system, which is arequierement for the efficiency of operation. The conventionalinstallations therefore generally contain, in addition to the saidreactor tank and settling tank, a recycling pump unit which takes careof recharging the said sludge-and-reagent mixture from the settling tankto the reactor tank.

It is the object of the invention to improve the conventional systems byproviding for control of the amount of the recirculated sludge.According to the invention the recycling of the sludge and reagent intothe reactor tank is realized without the need for a separate pump unit,ensuring at the same time the intense blending of the components in thereactor tank, and the oxygen supply necessitated for the biologicalprocesses.

The known systems for waste water purification with biologicallyactivated sludge can be classified into three main categories, viz.

l. rotary brush systems with horizontal axis,

2. systems based on air introduction, with superficial or deeppenetration,

3. superficial aeration by means of vanes disposed on a vertical shaft.

In the case of industrial wastes generally propeller type or cage typemixers are used. These mixing devices achieve thorough blending of themixture and, if required, the oxygenation of the mixture.

For the operation of the whole purification installation, however, inall these cases the previously described separate recycling pump unit isrequired. The invention, on the contrary, permits to ensure all therequirements of the operation of the reactor tank at an optimum level,while at the same time providing for the sludge and reagent recycledfrom the settling tank to be automatically recharged into the reactortank without the need for a specially installed pump unit.

In order to promote the better appreciation of the invention, theoperation of conventional waste water purification installations as wellas the attempts to eliminate the recycling pump units are describedbelow. In the conventional water purification installations the wastewater is fed through a conduit to the reactor tank, where the mixture ofsludge and water is continuously stirred, with simultaneous oxygenationof the activated sludge required for the purifying operation. Thethoroughly blended mixture is conveyed through a tube to the settlingtank, where the sludge separates from the water by gravity and settlesat the bottom. A scraper conveys the settled sludge to the slurry bed(sump), whence it is recharged by the recycling pump through a pipe tothe reactor tank.

The construction of a recycling pipe and a pump unit is not only costlybut also constitutes a number of sources of error. It has therefore beenrepeatedly attempted to dispense with these components. According to oneof these suggestions the water-sludge mixture contained in the reactortank is continually agitated by a mixing device. Mixing is performed byair injection, the air being blown in through an air injector disposedalongside one of the side walls. The mixture thus blended passes throughan aperture in the longitudinal side of the tank into a settling tankwhere the sludge is caused to settle.

Theoretically such installations are self-adjusting, since the settledsludge slides back to the reactor tank through the apertures, but inactual practice the efficiency of recycling is not satisfactory, sincerecharging of the sludge is effected in a direction contrary to thedischarge of water. A further disadvantage of these installations isthat the pulsating movement of the water in the reactor tank propagatesto the settling tank, and thus impedes, the procedure of settling.

For these reasons the described type of installation could only beutilized in exceptional cases, that is, when the efficiency of sludgerecycling is not of importance, or when a relatively small settling tankis required in relation to the oxygenation tank.

In order to eliminate the said drawbacks of the known apparatus,according to the invention the installation comprises a reactor oroxygenating tank, a settling tank, a vertical pipe provided in theoxigenating tank, a mixing device extending into the upper portion ofsaid vertical pipe, a pipe line conveying the blended mixture of sludgeand water from the oxygenating tank into the settling tank, and thisinstallation is characterized by a conduit connecting a slurry bed ofthe settling tank with the oxygenating tank, wherein the extremity ofthe conduit introduced into the tank reaches into the center axis of thesaid vertical tube provided in the center line of the tank and protrudesto a slight extent into said tube, and slots of adjustable size areformed by the lower edge of the vertical tube and the bottom plate ofthe oxygenating tank.

A preferred embodiment of the apparatus according to the invention ismore particularly described below with reference to the accompanyingdrawings, in which FIG. 1 is a schematic vertical section through theentire installation,

FIG. 2 is a side view on an enlarged scale of the turbine wheel or rotorof the oxygenating tank, while FIG. 3 is a top view of said turbinewheel.

The mixture of water and sludge contained in the tank 1 is vigorouslystirred by means of the mixing device 2, a process which also providesthe oxygen supply required for the biological processes taking place inthe oxygenation tank. The mixing device is disposed in a tube 3 runningvertically centrally in the oxygenation tank, and reaching almost downto the bottom of said tank. The thoroughly blended mixture passesthrough a pipe 4 to a settling tank 5, where the sludge settles. Thesettled sludge is conveyed by a scraper means to a slurry bed or sump 7.The slurry bed 7 is connected by a pipe 8 with the oxygenation tank 1.Said pipe 8 enters the tank 1 in vertical direction exactly where thebottom is intersected by the axis line;

the extremity 9 of the pipe 8 conveniently protrudes into the tube 3, soas to produce an increased suction effect.

The operation of the installation according to the invention for thepurification of waste waters by means of activated sludge is as follows:

When the mixing device 2 starts working in the oxygenation tank 1, itacts as a pump, so that a vast amount of water is sucked up from thetube 3 and spread over the entire water surface. This intense agitationgives rise to a complete mixing or blending of the contents of the tank,at the same time providing the necessary oxygen supply, as well aspreventing the settling of the sludge.

Fresh quantities of water penetrate into the tube 3 through anadjustable slot 10, to replace the large amount of liquid sucked up bythe tube 3. The slot 10 is formed by the lower edge of the tube 3 and bythe bottom of the tank. As a result a circulation is provided within theliquid contained in the tank 1 in the flow direction indicated by thearrows. The flow of liquid sucked up by the tube 3 is countered by theresistance which is defined by the dimensions of the slot and the amountof liquid, said resistance increasing quadratically with the increase ofthe amount of liquid to be treated. In order to vary the size of theslot, the lower extremity of the tube 3 may be shortened or lengthenedtelescopically.

If the conveying efficiency of the mixing device 2 is slowly increased,or if the size of the slot 10 is reduced, the resistance of the fluidpassing through the slots will increase to such an extent as to exceedthe resistance of the pipe 8 running from the bottom of the oxygenatingtank 1 to the slurry bed 7 of the settling tank 5. In this case thestreaming of the liquid through the pipe 8 is started, which essentiallyconstitutes the recycling or recirculation from the slurry bed 7 to theoxygenating tank 1. Thus, the extremity 9 of the pipe 8 and the mixingdevice 2 set up axially in the tube 3 must be designed in such a manneras to perform the thorough blending of the water-sludge mixture in thetank 1 on the one hand, and to supply the oxygen necessary for thebiological processes which are to take place for activating the sludgeon the other hand, together with a considerable and concentrated suckingeffect in axial direction.

The operation of the installation according to the invention is simpleand highly economical, since it dispenses with the conventionalrecycling pump units and, accordingly, with the attendance required foroperating such pump units.

The turbine wheel represented in FIGS. 2 and 3 is a preferableembodiment of the mixing device. This embodiment consists of an aeratingdevice with a vertical axis, during the rotation of which air is suckedaxially from above, with simultaneous suction of liquid from below. Thevanes carry out the thorough blending on the sucked-in air and liquid,while at the same time the device gives rise to intense superficialwater motion and spraying together with a powerful turbulent action. Allthese efiects are produced by designing the aerating device andespecially the turbine wheel in accordance to the invention.

It is to be pointed out that for the same purpose there have been knownaerating apparatus or devices of unmovable construction, based on theprinciple of pressuiized air injection, also dynamical aerating deviceswith horizontal-shaft for superficial aeration, but none of these hasthe same advantageous effect as the superficial rotors with verticalaxis, called aerators. The device illustrated in FIGS. 2 and 3 belongsto this latter type.

A driving mechanism mounted on a bridge construc tion connected to theupper end of the vertical shaft rotates the aerating turbine wheel,whereupon the body of water carries out a turbulent motion. The motionof said water body is in the upward, axial direction, from the bottom ofthe tank, and passes helically downward near the sidewalls of the tank.An intense motion is produced on the surface of the water, which has theeffect of filling this water layer with oxygen. As a result of thestrong turbulence in the tank, the oxygen taken up on the surface of thewater is mixed with the entire volume body of water in the tank.

Three concentric disks are mounted on the vertical shaft 11, of whichthe lower disk 12 and the upper disk 13 have slots 14 and 15respectively, of conveniently identical size, whereas the central disk16 is provided with circumferentially disposed apertures 17, preferablyarranged along a circle. Symmetrically arranged, arcuate and perforatedvanes 18 are fixed to the concentric disks 12,13, these vanes 18extending beyond the concentric disks radially in outward direction,while inwardly they extend as far as the diameter corresponding to theapertures 14 and 15. Thus the inner space of the body of the wheel isdivided by the vanes 18 into intercommunicating chambers of inwardlytapering cross section.

The generatrix of the vanes considered as cylindrical surfaces, runsparallelly to the shaft 1 1, and their vertical dimensions areconveniently identical with or exceeding the vertical dimensions of thewheel body consisting of concentric disks. The vanes have downwardextending blades which may be pointed (FIG. 2) or trapezoidal (FIG. 1).The blades serve to impart movement to the liquid and this effect can beregulated, since the upper part of the tube 3 may be telescopicallyraised and lowered (FIG. 1).

With this design of the wheel or rotor the body of the latter is dividedin two, by means of the concentric disk 16 disposed in the middle. Inthe room 20 over the disk 16 the depression produced by the rotation ofthe turbine wheel has the effect of sucking in air axially from above;the suction effect in the lower part 21 below the disk 16 gives rise toa likewise axial sucking up of liquid. This results in an intimateblending of the sucked-up liquid, along the circumference of the vanes,whereby the desired oxygenation is performed.

The turbine wheel is disposed near the surface of the water. Duringrotation of the turbine wheel, i.e., the the vanes displace the upperportions of the liquid and exert a simultaneous spraying effect; asuction effect is moreover performed. All this results in a completemixing of the liquid in the tank, which is in turn equivalent to anintense oxygenation. In addition to these effects large amounts of airare sucked in simultaneously through the apertures 14 in the upper disk,andv 17 in the lower disk, respectively.

The mixing device may be disposed at different points of the verticalaxis. In some cases it may be of advantage for the liquid level 22 to beslightly below the upper edges of the vanes in the position of rest.During operation the water level will be shaped more or less like thewavy line 23 in FIG. 2.

As a result of the intense motion of the revolved water body thesucked-in air contacts the liquid in the form of fine air droplets, thussaturating the liquid with oxygen. The amount of oxygen so introduced isconsiderable, and increases the efficiency of the installationsubstantially.

The turbine wheel according to the invention therefore has a threefoldpurpose:

a. a powerful whirling and spraying of the water on the surface of theoxygenating tank 1,

b. an effective supply of oxygen from the atmosphere,

c. vigorous turbulence by means of the axially upwards directed effectof liquid suction.

The data resulting from the experiments made in connection with theinvention have clearly shown that the efficiency of the turbine wheeldesigned according to the invention is considerably higher than that ofthe known apparatus, for the reason that in addition to the vigorouswhirling of the water surface and the spraying, large amounts of the airfrom the atmosphere are sucked up in the above described manner, wherebythe efficiency of oxygen supply is substantially improved. Moreover,experiments have shown that the turbulence caused in the oxygenatingtank by the turbine wheel is very much stronger than in similar knownconstructions.

The above stated advantages, i.e., improved turbulence and ample oxygensupply account for a very high output of the method of oxygenationaccording to the invention. This presents itself already in thedimensioning when building new installations and, accordingly, in thereduced costs of construction. On the other hand, the capacity ofexisting, overloaded installations may be increased by means ofrelatively simple measures and without any considerable investment.

Since the rotation of the wheel gives rise to a considerable suction ofliquid in axial upward direction, the use of the turbine wheel accordingto the invention in installations where such suction eflect is anywayrequired for instance by means of a separate recycling pump unit isextremely useful, since the wheel induces such suction efl'ect withoutspecial measures and devices.

YVe claim:

Sewage treatment apparatus, compnsmg an oxygenating tank a settlingtank, hollow elongated means in said oxygenating tank for recirculating,circulating, blending and oxygenating sludge and water, first conduitmeans connecting said oxygenating and settling tanks for conveying theblended mixture of sludge and water from the oxygenating tank to thesettling tank, second conduit means connecting said oxygenating andsettling tanks for the pumpless recirculation of mainly settled sludgefrom the settling tank to the oxygenating tank and said elongated meanstherein, and adjustable means operatively connected to said elongatedmeans for varying to a substantial extent the amount of the circulatingwater and sludge mixture which enters said elongated means from theoxygenating tank.

2. The sewage treatment apparatus of claim 1, wherein said elongatedmeans comprises at least one tube the position of which is variablerelative to the bottom of the oxygenating tank.

3. The sewage treatment apparatus of claim 2, wherein the bottom edge ofsaid vertical tube and the bottom of said oxygenating tank define slotsof adjustable size.

1. Sewage treatment apparatus, comprising an oxygenating tank a settlingtank, hollow elongated means in said oxygenating tank for recirculating,circulating, blending and oxygenating sludge and water, first conduitmeans connecting said oxygenating and settling tanks for conveying theblended mixture of sludge and water from the oxygenating tank to thesettling tank, second conduit means connecting said oxygenating andsettling tanks for the pumpless recirculation of mainly settled sludgefrom the settling tank to the oxygenating tank and said elongated meanstherein, and adjustable means operatively connected to said elongatedmeans for varying to a substantial extent the amount of the circulatingwater and sludge mixture which enters said elongated means from theoxygenating tank.
 2. The sewage treatment apparatus of claim 1, whereinsaid elongated means comprises at least one tube the position of whichis variable relative to the bottom of the oxygenating tank.
 3. Thesewage treatment apparatus of claim 2, wherein the bottom edge of saidvertical tube and the bottom of said oxygenating tank define slots ofadjustable size.